With development of electronic technologies, daily life and work of people rely more on portable mobile devices, for example, mobile phones, tablet computers, digital cameras, and mobile power packs. Power cables and data cables of such portable mobile devices mostly use a universal serial bus (USB) cable shown in FIG. 1. Therefore, people usually carry a USB cable with them in case of need. However, portability of the USB cable shown in FIG. 1 is relatively poor. Moreover, such conventional USB cables are different in length and thickness, making it difficult to bundle and neaten, and causing a lot of trouble to trips of people. At present, wearable devices become more popular, and are easy to carry, but such a feature fails to bring convenience to other devices.